FWIW I got one of those JBL package deals from Boater's World. Made even better with the 0% financing, which I paid off before any fees were due.
This model MR4B came with one of those water-resistant mouting boxes that I mounted over the helm station. Easy to use, and when the faceplate is removed, a red LED flashes in the box so it makes it look like the boat is alarmed. OK, just checked, they don't have the 'full package' anymore, as least on their website.
This is the head unit I bought
click here. It came with just 2 speakers, so I added 2 other 6" round ones by Sony, that were billed as waterproof. The JBLs sound nicer, but I am sure that is becuase they are reflecting off of the interior. The Sonys have been fool-proof to date out in the cockpit, mounted low on the side bulkheads of the cabin rear.
Plus I LOVE IT with the wired remote that lets me run it from my 2nd control station
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